/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.io;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.annotations.Experimental.Kind;

import com.bff.gaia.unified.sdk.io.fs.CreateOptions;

import com.bff.gaia.unified.sdk.io.fs.MatchResult;

import com.bff.gaia.unified.sdk.io.fs.ResourceId;



import java.io.FileNotFoundException;

import java.io.IOException;

import java.nio.channels.ReadableByteChannel;

import java.nio.channels.WritableByteChannel;

import java.util.Collection;

import java.util.List;



/**

 * File system interface in Unified.

 *

 * <p>It defines APIs for writing file systems agnostic code.

 *

 * <p>All methods are protected, and they are for file system providers to implement. Clients should

 * use {@link FileSystems} utility.

 */

@Experimental(Kind.FILESYSTEM)

public abstract class FileSystem<ResourceIdT extends ResourceId> {

  /**

   * This is the entry point to convert user-provided specs to {@link ResourceIdT ResourceIds}.

   * Callers should use {@link #match} to resolve users specs ambiguities before calling other

   * methods.

   *

   * <p>Implementation should handle the following ambiguities of a user-provided spec:

   *

   * <ol>

   *   <li>{@code spec} could be a glob or a uri. {@link #match} should be able to tell and choose

   *       efficient implementations.

   *   <li>The user-provided {@code spec} might refer to files or directories. It is common that

   *       users that wish to indicate a directory will omit the trailing {@code /}, such as in a

   *       spec of {@code "/tmp/dir"}. The {@link FileSystem} should be able to recognize a

   *       directory with the trailing {@code /} omitted, but should always return a correct {@link

   *       ResourceIdT} (e.g., {@code "/tmp/dir/"} inside the returned {@link MatchResult}.

   * </ol>

   *

   * <p>All {@link FileSystem} implementations should support glob in the final hierarchical path

   * component of {@link ResourceIdT}. This allows SDK libraries to construct file system agnostic

   * spec. {@link FileSystem FileSystems} can support additional patterns for user-provided specs.

   *

   * @return {@code List<MatchResult>} in the same order of the input specs.

   * @throws IllegalArgumentException if specs are invalid.

   * @throws IOException if all specs failed to match due to issues like: network connection,

   *     authorization. Exception for individual spec need to be deferred until callers retrieve

   *     metadata with {@link MatchResult#metadata()}.

   */

  protected abstract List<MatchResult> match(List<String> specs) throws IOException;



  /**

   * Returns a write channel for the given {@link ResourceIdT}.

   *

   * <p>The resource is not expanded; it is used verbatim.

   *

   * @param resourceId the reference of the file-like resource to create

   * @param createOptions the configuration of the create operation

   */

  protected abstract WritableByteChannel create(ResourceIdT resourceId, CreateOptions createOptions)

      throws IOException;



  /**

   * Returns a read channel for the given {@link ResourceIdT}.

   *

   * <p>The resource is not expanded; it is used verbatim.

   *

   * <p>If seeking is supported, then this returns a {@link java.nio.channels.SeekableByteChannel}.

   *

   * @param resourceId the reference of the file-like resource to open

   */

  protected abstract ReadableByteChannel open(ResourceIdT resourceId) throws IOException;



  /**

   * Copies a {@link List} of file-like resources from one location to another.

   *

   * <p>The number of source resources must equal the number of destination resources. Destination

   * resources will be created recursively.

   *

   * @param srcResourceIds the references of the source resources

   * @param destResourceIds the references of the destination resources

   * @throws FileNotFoundException if the source resources are missing. When copy throws, each

   *     resource might or might not be copied. In such scenarios, callers can use {@code match()}

   *     to determine the state of the resources.

   */

  protected abstract void copy(List<ResourceIdT> srcResourceIds, List<ResourceIdT> destResourceIds)

      throws IOException;



  /**

   * Renames a {@link List} of file-like resources from one location to another.

   *

   * <p>The number of source resources must equal the number of destination resources. Destination

   * resources will be created recursively.

   *

   * @param srcResourceIds the references of the source resources

   * @param destResourceIds the references of the destination resources

   * @throws FileNotFoundException if the source resources are missing. When rename throws, the

   *     state of the resources is unknown but safe: for every (source, destination) pair of

   *     resources, the following are possible: a) source exists, b) destination exists, c) source

   *     and destination both exist. Thus no data is lost, however, duplicated resource are

   *     possible. In such scenarios, callers can use {@code match()} to determine the state of the

   *     resource.

   */

  protected abstract void rename(

      List<ResourceIdT> srcResourceIds, List<ResourceIdT> destResourceIds) throws IOException;



  /**

   * Deletes a collection of resources.

   *

   * @param resourceIds the references of the resources to delete.

   * @throws FileNotFoundException if resources are missing. When delete throws, each resource might

   *     or might not be deleted. In such scenarios, callers can use {@code match()} to determine

   *     the state of the resources.

   */

  protected abstract void delete(Collection<ResourceIdT> resourceIds) throws IOException;



  /**

   * Returns a new {@link ResourceId} for this filesystem that represents the named resource. The

   * user supplies both the resource spec and whether it is a directory.

   *

   * <p>The supplied {@code singleResourceSpec} is expected to be in a proper format, including any

   * necessary escaping, for this {@link FileSystem}.

   *

   * <p>This function may throw an {@link IllegalArgumentException} if given an invalid argument,

   * such as when the specified {@code singleResourceSpec} is not a valid resource name.

   */

  protected abstract ResourceIdT matchNewResource(String singleResourceSpec, boolean isDirectory);



  /**

   * Get the URI scheme which defines the namespace of the {@link FileSystem}.

   *

   * @see <a href="https://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>

   */

  protected abstract String getScheme();

}